The Value of Research in Comparative Cognition
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2018, 31 Charles I. Abramson Special Issue Editor Peer-reviewed The Value of Research in Comparative Cognition Thomas R. Zentall University of Kentucky, U.S.A. Most research in the field of comparative cognition has focused on the degree to which cognitive phenomena that have been reported in humans, especially children, can also be demonstrated in other animals. The value of such comparative research has not only been the finding that other animals show behavior that is qualitatively similar to that of humans but because the comparative approach calls for the careful control of variables often confounded with the mechanisms being tested, the comparative approach has identified procedures that may also improve the design of research with humans. The comparative approach has also been used to study the degree to which other animals demonstrate human biases and suboptimal behavior (e.g., commercial gambling). When applied to this field of research, the comparative approach has generally taken the position that human biases thought to be established by complex social and societal mechanisms (e.g., social reinforcement and entertainment) may be more parsimoniously accounted for by simpler mechanisms (i.e., conditioned reinforcement and positive contrast). When explained in terms of these mechanisms, the results have implications for explaining in simpler and more general terms the results of similar research with humans. Thus, comparative psychology tells us not only about the similarities and possible differences in behavior among species but it also may have implications for our understanding of similar behavior in humans. Comparative cognition is an area of comparative psychology that deals with the relation between the learning of humans and other animals (Beran, Parrish, Perdue, & Washburn, 2014). Traditionally, learning implies changes in behavior governed by Pavlovian and instrumental conditioning, together with primary stimulus generalization, and although cognition implies a broad range of learning processes, it has typically been borrowed from research with humans to suggest an attempt to describe possible internal states or representations that result in the behavior observed. As the description of internal states cannot be observed directly, comparative cognition research often attempts to distinguish between simple associative processes and more complex processes generally attributed to humans. Although the term cognition has been defined in various ways, for the present purposes it will be defined as acquired behavior that cannot be explained by simple associative processes, including stimulus generalization along physical dimensions (Tolman, 1948). Comparative cognition research begins with the premise that behavior has evolved for the survival and reproductive success of organisms and given the fact that many of the behavioral demands of survival of different organisms have been similar, the processes that underlie those behaviors may be similar as well (Beran et al., 2014). Whether those processes exist in other animals, or even in humans for that matter, is an empirical question but it should not be assumed that they are unique to humans. The goal of this article is twofold: first to present several examples of research in comparative cognition to determine whether or not they can be accounted for with relatively simple learning mechanisms and second to ask whether contexts in which humans are known to choose suboptimally can also be found in other animals. In the case of human suboptimal choice, if similar behaviors can be demonstrated in other animals, can they be explained by relatively simple learning mechanisms? And if they can, is it possible that the same mechanisms are responsible for similar behavior when it occurs in humans (see e.g., Epstein, Lanza, & Skinner, 1981). Many of the examples described in this article come from research with pigeons. This is in part because extensive research has been conducted with pigeons because of their excellent vision and visual Please send correspondence to Thomas R. Zentall, Department of Psychology University of Kentucky Lexington, KY 40506 (Email: [email protected]) stimuli are easy to obtain and present. Paradoxically, research on comparative cognition has often studied pigeons because they are so different from humans that if certain cognitive abilities can be demonstrated in pigeons it is likely that they can be found in other species as well. Methodological Problems In comparing the learning abilities among animals one encounters the problem of distinguishing differences in cognition from differences in perception (the ability to process sensory stimuli). When compared to humans, many mammals do not have well developed color vision and nocturnal species depend primarily on their auditory and olfactory senses. Species also differ in the kind of responses that they can make. For example, most primates have the ability to respond by grasping objects, whereas other species have more limited ability to make a response (e.g., with a paw or a beak). Bitterman (1975) has suggested an experimental means of bypassing the input-output limitations of species comparisons that he suggests should compensate for differences in sensory capacity, motor responding, and even motivation to participate. He suggests that rather than looking for differences in the rate at which different species can learn, we might look at differences, for example, in an animal’s ability to learn from the experience of learning (Harlow, 1949). In other words, to what extent can learning facilitate new learning (learning to learn)? For example, an animal may be trained to make a simple discrimination (e.g., between black and white) and then the discrimination may be reversed repeatedly. Then, using the rate of original learning as a baseline, one can determine the degree to which later learning (reversals), presumably involving the same processes, is facilitated. Sometimes an approach that appears to be a logical, however, is not always psychological. The general finding from research with visual discriminations is that monkeys show more improvement with reversals than rats, and rats show more improvement that pigeons. Surprisingly, however, if the discriminations are olfactory, rats show better improvement over reversals than monkeys do with visual discrimination (Slotnick & Katz, 1974). Thus, even with these learning-to-learn measures, it may be difficult to make quantitative comparisons among species. Such findings also suggest that the failure to find evidence that a given species has a particular cognitive ability is not evidence that it does not have such an ability. It may be necessary to use other procedures, modalities, dimensions, or stimulus differences to demonstrate it. The Problem of “Instructions” An important problem that often occurs in evaluating the cognitive capacity of animals is distinguishing between what an animal understands the task to be and its ability to perform the task (see Zentall, 1970, 1997). When assessing the cognitive capacity of humans, subjects are typically given instructions about the nature or demands of the task. If humans are asked to learn a list of words and tested for their memory at a later time, they may be instructed to recall as many words they can remember from the list that they learned earlier. Assuming that animals had learned to make a series of responses, it is not clear how they would be given instructions to reproduce the set of responses that they had learned earlier. With animals the context may act as a cue to “do what you did in this context earlier” (Zentall, 1970), but the context may not provide an unambiguous cue. Attempts to study pigeon working memory for temporal durations provides an interesting example of how one can misinterpret the results of an experiment because of the problem of inadequate “instructions.” Pigeons can learn a temporal discrimination in which after a short duration (2 s) stimulus (sample), choice of a red comparison stimulus is correct but after a longer duration (8 s) stimulus, choice of a green comparison 2 stimulus is correct. When working memory for sample duration is assessed by inserting a delay between the offset of the sample and the onset of the comparison stimuli, unexpected retention functions have been found. As the delay increases, the retention function (probability of being correct) for the long sample declines rapidly, quickly falling below chance, whereas the retention function for the short sample declines hardly at all (see Figure 1a). This finding of divergent retention functions with increasing delay, referred to as the choose-short effect (Spetch & Wilkie, 1983), has been attributed to the subjective shortening of memory for duration as a function of the time since the duration was presented (Spetch & Sinha, 1989). The idea is, as the delay increases, the long duration stimulus would be increasingly remembered as being shorter and at some point would be responded to as if it was the shorter one, whereas the shorter duration stimulus would never be remembered as being longer. The problem with the subjective shortening account is because the delays are novel events, and typically they are dark intervals, similar in appearance to the time between trials (the intertrial interval), the way animals treat the delay trials may be different from the way their behavior is interpreted. Imagine that the animals interpret the delay as the end of the trial and the appearance of the comparison stimuli as choice on the next trial (that would have occurred without a sample duration). The closest duration to no duration would have to be the short duration, hence a choose short effect and the longer the delay the more certain the pigeon would be that the trial was over. One way to disambiguate the delay would be to make the intertrial interval distinctive from the dark delay by turning on the houselight. When that has been done, the retention functions have been found to be quite parallel (see Figure 1b; Dorrance, Kaiser, & Zentall, 2000). This finding suggests that the divergent retention functions may result, at least in part, from the ambiguity of the meaning of the novel delays.